The self-assembly technique experimented for the deposition of alkanes and alkyl derivatives on layered compounds at the liquid/solid interface has been successfully extended to the adsorption of poly(3-decyl-thiophene) on graphite. The molecular films so obtained have been investigated using scanning tunnelling microscopy (STM). Images taken in both the constant-current and constant-height modes show highly packed arrays of molecules characterised by an average length and an average spacing that are in good agreement with results obtained by X-ray diffraction investigations. Constant-current images allow one to observe domain formations in preferential directions coincident with the main axes of the graphite lattice, while constant-height imaging, performed on small areas, allows one to resolve atomic structures within the polymer backbone. In particular, periodic, 0.71 nm spaced features have been identified along the side of the polymer backbone; they can be associated with the length of two monomer units and are attributable to imaging of sulphur atoms in the backbone.